In recent years, thin and hollow flattened products such as heat collecting plates of a solar water-heating device, casings of office automation equipments, panels, furnitures and interior decorations are experimentally blow molded. In such cases, as shown in FIG. 33 of the accompanying drawings, cylindrical parison "a" is extruded downward, sandwiched by thin metallic molds "b" and "c" from left and right and air is blown therein, as a common blow molding machine does. As a result, the parison "a" expanded due to air injection is fixed at its part "a1" which first contacts an inner wall of the metallic mold and expands therefrom to left and right so that a product having a uniform thickness (wall thickness) cannot be obtained. Thereupon, the present applicant previously developed a flat blow molding machine which does not extrude the cylindrical parison "a", but extrudes hollow flattened parison, that matches an inner wall of thin metallic molds "b" and "c", from clearance between a planar flattened core and a flattened die surrounding the core so as to mold a hollow plate-like product having a uniform thickness.
This type of flat blow molding machine is constructed as follows, as shown in FIG. 34: an accumulator chamber "e" whose section is flattened is formed in a housing "d" in a vertical direction, a planar flattened mandrel "f" is vertically provided at the center of the accumulator chamber "e" and a flattened piston "g" is fitted over the flattened mandrel "f". The flattened piston "g" is lowered by a hydraulic cylinder "h" to pressurize the resin in the accumulator chamber "e" and the pressurized resin is extruded in the form of hollow flattened parison "k" from clearance between a flattened core "i" provided at a tip of the flattened mandrel "f" and a flattened die "j" provided at a lower end of the housing "d". The resin is fed to the accumulator chamber "e" from extruders "q" provided on left and right sides in its thickness Y direction. The flattened parison "k" extruded as shown in FIG. 35 is sandwiched by flattened metallic molds (not shown) in a direction perpendicular to the drawing sheet and air is blown therein.
However, conventional flat blow molding machines have the following problems:
(1) since the width of the extruded parison "k" cannot be adjusted, an unnecessary portion of the extruded flattened parison "k" should be collapsed by the metallic mold and the molded products inevitably have flashes when flattened products having a width smaller than the width of the parison "k" should be manufactured. In other words, a flash ratio is raised and this is not economic; PA1 (2) in order to blow mold two products each having a width smaller than the flattened parison "k", unnecessary parison "k" should be collapsed by the metallic mold and the products should have flashes, as shown in FIG. 36. Specifically, in order to obtain two molded products having a reduced width "n" and "o", the unnecessary parison "k" between these two products "n" and "o" should be crashed by the metallic mold so that unduly large flashes "p" are produced. Therefore, this is not preferred if material expense and manufacturing cost are concerned, i.e., it raises problems in terms of resource saving and energy saving; PA1 (3) since two extruders "q"s are located left and right in the width Y direction of the flattened accumulator chamber "e" having a width X and a thickness Y and the resin extruded therefrom is introduced to the accumulator chamber "e" from a center of left and right flattened faces of the flattened piston "g", the resin pressure in the accumulator chamber "e" does not become uniform. Specifically, since the resin pressure at the center in the width X direction of the flattened accumulator "e" is relatively high due to small clearance to the extruder "q", the resin pressure at ends in the width X direction of the flattened accumulator chamber "e" is low due to large clearance to the extruder "q". In this manner, the resin which fills the flattened accumulator "e" has a pressure distribution that is high at the center and low at both ends in the width X direction. Accordingly, if such resin is injected from an injection opening "m" between the flattened die "j" and the flattened core "i", the extruded flattened parison will have bending caused by the above-mentioned pressure profile; PA1 (4) the flattened mandrel "f" is moved up and down by an actuator "l" during the injection of the flattened parison "k" to adjust the clearance between the flattened core "i" and the flattened die "j" (gap control) and to control the thickness of the parison "k" in the injection direction. In this case, since the accumulator chamber "e" is filled with the resin, the flattened mandrel "f" should be moved up and down with a force overcoming the resin pressure. However, the flattened mandrel "f" which is molded to be a wide and planar one easily bends due to insufficient rigidity. Further, the flattened mandrel "f" may be offset from the center of the accumulator chamber "e" in a range of slide face allowance of the flattened piston "g" and the flattened mandrel "f". If the flattened mandrel "f" is offset or bends as mentioned above, the clearance between the flattened core "i" located at the tip of the mandrel "f" and the flattened die "j" located at the lower end of the housing "d" varies so that the thickness of the injected flattened parison "k" becomes non-uniform. This makes a bending portion in a product so that sound blow molding cannot be expected. In addition, this causes abnormal abrasions and scratching on the slide face; PA1 (5) in order to avoid mixing of colors and/or materials upon change of color and/or material of the resin (parison), the housing should be disassembled and the resin adhering on the interior should be cleaned off. For example, if the color of the resin is changed to white from black, a trace amount of black resin remaining in the housing may cause the color mixing in a product. Thus, the resin adhering on the interior of the housing must be completely removed. However, disassembling the housing of the blow molding machine requires a large crane and/or a complicated lifting device so that operations are troublesome and take time. In case of color change or material change, alternatively, the resin is allowed to flow out of the molding machine till the color or the material of the injected parison changes, instead of disassembling and cleaning the housing. However, this requires a large amount of resin for replacement if the resin should be replaced to low viscosity resin from high viscosity resin or white resin from black resin. Further, this approach may result in color and material mixing in the product so that it is not employable and is extremely costly; PA1 (6) the injected hollow flattened parison "k" expands due to swell effect of the resin as shown in FIG. 37 upon injection to the atmosphere from the accumulator chamber "e" of high pressure. Specifically, it expands from the injection opening "m" between the flattened die "j" and the flattened core "i" shown in FIG. 34(c), with a short edge-to-long edge ratio of its section being reduced. Therefore, the expanded parison "k" does not match the inner wall of the thin metallic molds "b" and "c" so that a blow molded product has a non-uniform thickness with an unnecessarily large thickness, like a case of circular parison. Moreover, if the injected flattened parison "k" has vertical wrinkles, pre-blow should be performed to eliminate them. However, if pre-blow air pressure is applied to the interior of the flattened parison "k", not only the swell effect but also the pre-blow air pressure cause the parison to expand. Thus, the parison "k" has an oval or circular section. In this case, the meaning of injecting the flattened parison "k" using the flattened die "j" and the flattened core "i" is lost. Further, if the flattened die "j" and core "i" having a large flattened ratio are used to inject the flattened parison "k", the resin section of the flattened parison "k2" injected as shown in FIG. 38 changes its shape due to the swell effect and drawdown. In this case, the left and right inner faces "k1" of the parison "k" may be fused and joined with each other in the direction of injection. This disables the blow molding; and PA1 (7) a curved (three dimensional) duct which has a plurality of passages in the longitudinal direction is employed in the fields of automobiles, house-use electric devices, sanitary equipments or the like. Conventionally, when this type of curved duct is manufactured by the blow molding, a plurality of parison is injected from a plurality of injection heads, part or all of which are fused. Alternatively, both sides of the parison injected into the metallic mold are sandwiched and pressed by pushing plates extending in the direction of injection to fuse the parison at the tip of the pushing plates. However, in the former approach, the apparatus becomes large since it employs a multi-injection head, and in the latter approach, grooves formed upon drawing of the pushing plates out of the parison deteriorate the strength and the appearance of the product.
A first object of the present invention which is developed in consideration of the above is to provide a flat blow molding machine which can change width of flattened parison injected from the molding machine.
A second object is to provide a flat blow molding machine which can reduce unnecessary flashes to raise the productivity when manufacturing a product having a width smaller than flattened parison injected from clearance between a flattened die and a flattened core.
A third object is to provide a flat blow molding machine which can uniformalize resin pressure in an accumulator chamber in a width direction so as to inject flattened parison having no bending.
A fourth object is to provide a flat blow molding machine which prevents bending and offsetting of a flattened mandrel so as to inject flattened parison having uniform thickness (wall thickness) and no bending.
A fifth object is to provide a blow molding machine which allows division of a housing for easy cleaning when color and/or material of the resin should be changed.
A sixth object is to provide blow molding method, apparatus and products which can prevent the injected hollow flattened parison from being deformed due to the swell effect and drawdown.
A seventh object is to provide curved blow molding method and product which can manufacture products using a small molding machine without deteriorating strength and appearance when a curved (three dimensional) blow molded product whose interior is divided in the direction of injection is manufactured.